Stabilization of Distal Femur Fractures with
Intramedullary Nails and Locking Plates:
Differences in Callus Formation
Christopher E. Henderson, MD,* Trevor Lujan, PhD,** Michael Bottlang, PhD,**
Daniel C. Fitzpatrick, MD,† Steve M. Madey, MD,† J. Lawrence Marsh, MD*
Abstract
Objectives: This study compared callus formation in distal femur fractures stabilized with locking
plates and intramedullar y nails to test the hypothesis that locking plates induce less fracture callus
than IM nails.
Design: Retrospective case matched study.
Setting: Two orthopaedic trauma centers.
Patients: 174 distal femur fracture were reviewed to extract cases treated with retrograde
IM nails (NAIL group, n=12). These were then
individually matched to cases treated with locking
plates (Plate group, n=12).
Inter vention: Retrograde IM nailing or locking
plate fracture fixation.
Outcome Measures: Periosteal callus was measured on lateral and antero-posterior radiographs
taken at 12 weeks after injur y using validated
software to objectively extract the size of peripheral
callus from digital radiographs.
Results: The NAIL group had 2.4 times more
callus area per location (231 ± 304 mm2) than
the PLATE group (95 ± 109 mm2, p=0.028).
Compared to the PLATE group, the NAIL group
had 3.4 times more callus anteriorly (p=0.31), 2.6
times more callus posteriorly (p=0.25), and 2.3
times more callus medially (p=0.16). At 12 weeks
after injur y, no or minimal callus for secondar y
bone healing (<20 mm2) was present in 20% of
callus locations in the NAIL group and in 54% of
callus locations in the PLATE group.
Conclusion: Significantly less periosteal callus
formed in fractures stabilized with locking plates
Orthopaedics and Rehabilitation, University of Iowa Hospital and
Clinics, Iowa City, IA 52242
**
Biomechanics Laboratory, Legacy Research & Technology Center,
Portland, OR 97232,
†
Slocum Center for Orthopaedics, Eugene, OR, 97401
Corresponding Author:
J Lawrence Marsh, MD
Department of Orthopaedics and Rehabilitation
University of Iowa Hospitals and Clinics
200 Hawkins Drive, Iowa City, IA 52242
Phone: (319)-653-0430; fax (319)-353-6754; email:j-marsh@uiowa.edu
*
than with IM nails. This result is likely multifactorial and further study of the interaction between
construct stif fness and fracture healing in the
distal femur is warranted.
Introduction
Fractures of the distal third of the femur are a treatment challenge despite new fixation options. Fixed angle
locking plates have become the most commonly used
device for this indication replacing intramedullary nails,
blade plates and condylar screws.1 Despite widespread
use, there are few studies that directly compare locking
plates to more traditional techniques.
Locking plates have been developed in conjunction
with a minimally invasive biologically friendly insertion
technique which allows the plate to be placed without
excessive soft tissue-stripping and with minimal disruption of the bone blood supply.1,2 Similar to intramedullary
nails these plates are used to span zones of comminution
which then must heal with an external callus. They have
been designed to limit fracture gap strain with physiologic loads and have improved fixation in osteoporotic,
cancellous, or comminuted bone.1-3
One concern with locking plate constructs is that
the high stiffness achieved may limit the amount of
callus, resulting in delayed healing or nonunion.4-6 For
comminuted fractures treated with a bridging technique,
peripheral callus is necessary for fracture healing.7-9 To
our knowledge there have not been any studies that
have directly compared the amount of callus formed
with locking plates to that formed with other implants
used to treat distal femur fractures such as intramedullary nails. Intramedullary nails have many of the same
advantages as locking plates such as percutaneous placement without disruption of blood supply, indirect fracture
reduction, success in osteoporotic bone and have been
reported to lead to high healing rates in fractures of the
distal femur.10-14 There is also evidence that intramedullary nails are less stiff than locking plates.15,16
The purpose of this study was to quantitatively
measure callus formation and use it as an outcome assessment to compare two clinical techniques used to
stabilize distal femur fractures. We hypothesized that the
increased stiffness of locking plate fracture constructs
leads to less fracture callus than similar constructs with
Volume 30 61
C. E. Henderson, T. Lujan, M. Bottlang, D. C. Fitzpatrick, S. M. Madey, J. L. Marsh
Table 1. Demographic and radiologic criteria used for patient matching are
reported demonstrating closely matched NAIL and PLATE pairs
intramedullary nails. This hypothesis was tested with a
retrospective case matched study design.
Patients and Methods
Approval from the investigational review board for
our institutions was obtained. Patients treated for distal
femur fractures between 1998 and 2006 at the University
of Iowa and Slocum Center for Orthopaedics were identified by searching the Current Procedural Terminology
(CPT) coding records of the hospital for distal femur
fracture repair. These diagnoses were confirmed by
review of the medical records. One hundred seventy
four distal femur fractures were initially identified. Of
these forty six were primarily fixed with a femoral retrograde intramedullary nail. Revision cases, periprosthetic
fractures below a total hip arthroplasty, patients with
incomplete records, missing or poor quality radiographs,
or follow up less than 12 weeks were excluded. Fifteen
patients met appropriate criteria (NAIL group).
62 The Iowa Orthopaedic Journal
Baseline characteristics of the patient and the fracture
were identified from the medical record including age,
gender, type of fracture fixation, open vs. closed fracture,
periprosthetic fracture (above total knee), and comorbidities such as diabetes and smoking. Injury radiographs were reviewed for OTA fracture classification,17
postoperative radiographs were reviewed to confirm
documented treatment, and 12 week anteroposterior and
lateral radiographs were used for callus measurement.
A comparison group of patients treated with locking
plates were identified from the original patient cohort
(PLATE group). The NAIL group of patients were individually matched to the patients treated with locking
plates according to OTA classification, age, gender, open
versus closed fracture, periprosthetic fracture, smoking,
and diabetes (Table 1). We accepted only exact matches
for OTA classification. Three NAIL patients did not
have an acceptable PLATE match and were not used.
All patients were exact matches for smoking status.
Stabilization of Distal Femur Fractures with Intramedullary Nails and Locking Plates
Eleven of 12 patients were exact matches based on open
versus closed fracture; one patient in the NAIL group
had a Gustillo type 1 open fracture and was matched to
a closed fracture in the PLATE group. Two of 12 patient
matches differed in the presence of diabetes. One periprosthetic fracture in the NAIL group was matched to a
nonperiprosthetic fracture in the PLATE group. Patient
age was matched closely however exact matches were
not possible. The average age difference among matched
patients was eight years and only three patient matches
differed by greater than 10 years. Four patients had all
variables matched, five had only a difference in gender,
and three had two variables unmatched, no patient pairs
had greater than two unmatched variables.
The patient charts and all available radiographs were
reviewed for complications including superficial or
deep infection, hardware failure or removal, malunion,
nonunion, need for revision surgery, and time to weight
bearing. Coronal alignment was measured as the angle
between a line bisecting the distal femur shaft and a line
parallel to the proximal tibial plateau. Normal coronal
alignment was considered 5˚-7˚ valgus, and normal sagittal alignment was neutral. Malalignment was defined as
greater than a 5˚ deviation from normal coronal or sagittal alignment. Loss of alignment was defined as greater
than a 3˚ change in angular measurements between
postoperative and follow-up radiographs.
The peripheral callus was measured on lateral and
antero-posterior radiographs at 12 weeks in all fractures
(Figure 1). The callus measurement technique has been
previously described and validated.6,18 Briefly, custom
software extracted the projected area of periosteal callus
by using regional pixel intensities and pixel gradients.
Callus size was converted from pixels to metric area
by using an implant feature of known dimension. The
algorithm has less than a 5% error in measuring callus
area and the algorithm strongly correlated with orthopaedic surgeons that manually traced the callus outline
(r=0.94).18 In the NAIL group, the projected callus area
at the anterior, posterior, medial and lateral location was
measured (41 fracture sites). In the PLATE group, callus
at anterior, posterior and medial locations was measured
(31 fracture sites). Callus at lateral locations could not
be measured since the plate was inserted on the lateral
cortex. If multiple fractures could be observed on one
cortical location, periosteal callus was measured at all
fracture sites and an average was taken.
The amount of callus at each location (anterior, posterior, medial) was compared between the NAIL and
PLATE group. Fractures were stratified by OTA classification, open vs. closed, and union vs. nonunion for
further comparison. Statistical analysis was performed
using Fisher’s exact test and Student’s t test. All com-
Figure 1. Periosteal callus measurement in matched plate and
nail cases at week 12. A) No periosteal callus on medial cortex.
B) Bridging periosteal callus on lateral cortex.
parisons were two-tailed and the significance level was
set at 0.05.
Results
The results of the chart review and matching process
are presented in Table 2. No significant differences were
found between the NAIL and PLATE groups baseline
characteristics. Ten fractures in each group were treated
with a minimally invasive approach with closed reduction
of the metaphyseal fracture, two fractures in each group
required open reduction of an articular component or
irrigation for open fracture. In the NAIL group seven
fractures were treated with Trigen retrograde femoral
nails (Smith and Nephew; Memphis, TN), four with
Stryker T2 retrograde nails (Stryker; Kalamazoo, MI),
one with a Synthes Retrograde Femoral Nail (Synthes;
Paoli, PA), and one with a GSH (Smith and Nephew;
Memphis, TN). All IM nails were crosslocked with a
range of one to four cross lock screws distally (avg = 2.3)
and zero (one nail) to two cross locks proximally (avg =
1.2). The nail diameters ranged from 11.5 - 13 mm (avg
= 12.6mm) and all nails were inserted after overreaming the canal by 0.5 to 1.5 mm (avg = 1.2). The locking
plates utilized included five Less Invasive Stabilization
System (LISS; Synthes: Paoli, PA), four Synthes LCP
compression plates (Synthes; Paoli, PA) and three PERILOC Distal Femur Plates (Smith and Nephew; Memphis,
TN). Of these plates, seven were constructed of stainless
steel (Synthes LCP compression plate, PERI-LOC Distal
Femur Plate) and five were titanium (LISS, Polyaxial
Volume 30 63
C. E. Henderson, T. Lujan, M. Bottlang, D. C. Fitzpatrick, S. M. Madey, J. L. Marsh
Table 2. Clinical results and complications comparing patients treated with
intramedullar y nails (NAIL) to locking plates (PLATE)
NAIL (averages)
Follow up
Age
67 weeks (12-144)
Weight
89 kg (57-109)
Fall - 10
MVC - 2
Mechanism of injury
Knee ROM
2º-97º
Time to weight bearing
97 kg (57-157)
Fall -10
MVC -1
Crush – 1
0º-99º
1/12 (8%)
Sagittal malalignment
∆ Alignment >3º
Delayed union
Secondary surgery
0.63
0
3/12 (25%)
0.59
0
1/12 (8%)
2/12 (17%)
0
0
4/12 (33%)
2- nonunion revision
2- crosslock removal
2/12 (17%)
1- nonunion revision
1- total knee arthroplasty
distal femur plate). The plates ranged in size from nine
to 13 holes, average plate size was 10 holes.
Several subgroups were analyzed in an attempt to
identify factors that may affect callus formation. We
found no obvious relationship between nail diameter,
amount of overreaming, canal fill, or the number of
proximal or distal crosslock screws. We also could not
identify a difference in callus formation in stainless
steel compared to titanium plates, or screw/hole ratio.
Statistical analysis was limited by small group numbers.
Peripheral callus was found to be significantly greater
in the NAIL group compared to the PLATE group at 12
weeks postoperatively. The average callus per fracture
location in the NAIL group was 233 mm2 and in the
64 The Iowa Orthopaedic Journal
0.77
0.54
1.0
1.0
1.0
1.0
1/12 (8%)
Nonunion
0.65
11 weeks
0
5º-10º coronal
malalignment
Infection
65 years (25-96)
12 weeks
p value
57 weeks (16-120)
63 yrs (23-87)
PLATE (averages)
1/12 (8%)
1/12 (8%)
0.64
PLATE group was 95 mm2 (p = 0.04) [Figure 2A]. The
NAIL group had more callus formation on the anterior,
posterior, and medial cortices (p = 0.25, 0.31, 0.16) [Figure 2B]. The NAIL group had 226 ± 236 mm2 of callus
on the lateral cortex. The largest amount of callus was
found at the medial cortex and the smallest amount of
callus was found at the anterior cortex in both groups.
In the 12 matched pairs, the NAIL group had a greater
average callus amount in eight of the pairs (67%) and
the PLATE group had a greater average callus amount
in four of the pairs (33%) at week 12 (p = 0.22).
The average amount of callus per femur varied widely
in both groups. The NAIL group varied from 37 mm2 to
953 mm2 (mean=231 mm2) and the PLATE group varied
Stabilization of Distal Femur Fractures with Intramedullary Nails and Locking Plates
Figure 2. Average callus size in NAIL and PLATE cases. A) The NAIL group had over 2-fold more callus than the PLATE group (p=0.04).
B) Distribution of mean callus area at each cortical location. Circular depiction of callus area scaled to the cross-sectional area of an average
human femur.29
from 0 mm2 to 227 mm2 (mean=87 mm2). Several of the
fractures in the NAIL group formed a large amount of
callus exceeding 500mm2 at a single anatomic site. No
fractures in the PLATE group formed this large amount
of callus.
A considerable number of fractures treated with locking plates formed no or very little callus. Ranking periosteal callus by size increments of 20 mm2 demonstrated
that 17/31 (55%) fracture sites (ant, post, med on AP and
Lateral radiographs) in PLATE cases had between 0-20
mm2 of callus, while only 9/41 (22%) fracture sites (ant,
post, med, lat on AP and Lateral radiographs) in NAIL
cases had between 0-20 mm2 of callus (p<0.01) [Figure
3A]. There were similar differences between the NAIL
and the PLATE groups at all anatomic locations with the
largest difference found anteriorly [Figure 3B].
There was no significant difference in peripheral
callus formation between open versus closed fractures.
Open fractures had an average of 135 mm2 compared
to 83 mm2 in closed fractures (p = 0.35). There was
no significant difference in callus between cases stratified by the OTA classification. The more comminuted
fractures were 33A3 - 103 mm2 and 33C3 - 125 mm2 and
the less comminuted 32A2 - 24 mm2 and 33C1- 89 mm2
(p=0.07). There were no hypertrophic nonunions, in fact
the four fractures that went on to nonunion formed very
little callus (Nail four: 40 mm2, Nail nine: 187 mm2, Plate
seven: 6 mm2, Plate nine: 0 mm2). One nonunion was in
an open fracture, two were in patients with diabetes, and
none of the nonunion patients were smokers. Two of the
nonunions were in a case matched pair. All of the nonunions occurred in the most comminuted classifications,
32A3 or 33A3. Given the small number of nonunions we
could not identify other obvious mechanical or biological
factors that contributed to this adverse outcome.
Discussion
Despite the widespread use of locking plates to fix
distal femur fractures, evidence has not emerged demonstrating that these devices are superior to previously
established methods. A systematic review comparing
traditional plating, intramedullary nails, and locking
plates found no observed differences between implants
in the rate of nonunion, infection, fixation failure, or revision surgery.19 However subgroup analyses suggested
an increased risk of fixation failure and revision surgery
with locking plates compared to conventional plates but
a reduced infection rate.19 Herrera et al. in a systematic
review of 29 case series with a total of 415 distal femur
fractures found a 1.5% rate of nonunion with intramedullary nailing compared to a 5.3% rate with locked plates.20
In a prospective study, intramedullary nails and locking
plates were found to have equivalent functional outcome
scores.14
Secondary bone healing requires only relatively stable
fixation that results in some interfragmentary movement
to stimulate callus formation.7 There has been recent
concern that locking plates may be too stiff suppressing
the callus necessary for bridging by secondary healing.4-6
In distal femur fractures treated with locked plates, Lujan
et al. demonstrated asymmetric callus, with the majority
of callus forming medially away from the plate where
there is more motion. Less callus was found with stiff
stainless steel constructs and those with more holes
Volume 30 65
C. E. Henderson, T. Lujan, M. Bottlang, D. C. Fitzpatrick, S. M. Madey, J. L. Marsh
Figure 3. Periosteal callus distribution: A) At 12 weeks post surger y, 54% of PLATE cases had no or ver y little callus (≤20 mm2).
B) Percentage of fractures with callus size greater than 20 mm2 at each cortical location.
filled compared to less stiff titanium constructs and
those with empty holes near the fracture gap.6 Sanders
et al. reported more nonunions in stainless steel plates,
23%, compared to titanium plates, 7% (p=0.05).4 Locking
plate constructs can be several fold stiffer than external
fixators and they can be as stiff as traditional plating
constructs designed to promote primary bone healing
by restricting interfragmentary motion.21-23
Biomechanical studies have evaluated the stiffness
and interfragmentary motion of intramedullary nails and
locking plate constructs, however there have been no
direct comparative studies. Bottlang et al. showed only
0.2 mm of motion with axial loading under body weight
with a locked plate construct.15 A study of gap motion
comparing short and long cross locked supracondylar
nails showed fracture gap motion ranging from 1.8 mm
to 13.6 mm depending on nail length and the number
of proximal cross lock screws.24 These studies indicate
that locking plates can be substantially stiffer than intramedullary nails but there have been other biomechanical
studies where the differences are less clear.15,16,25,26 Locking plate constructs appear to have an asymmetric but
greater axial displacement than nails with varus loading,
however nails have greater total gap motion, especially
in response to torsion and shear stress resulting in increased shear strains.15,16,24-26
In this case matched study an overall smaller amount
of callus was formed by fractures treated with locking
plates and there were a greater number of plate cases
that formed little or no callus in the absence of identifiable biologic differences. In comparison to intramedullary fixation, a locking plate fracture construct may
decrease the amount of callus formation by limiting
66 The Iowa Orthopaedic Journal
interfragmentary motion. The fractures that failed to
unite formed very little callus indicating that bridging
periosteal callus is necessary for fracture healing. We
found that the least callus was anterior in our plated fractures and the most callus was medial. The anterolateral
position of the locking plate may limit the callus formed
anteriorly and laterally by proximity of these cortices
to the plate with increased local stiffness relative to the
medial cortex which is farther from the plate. The IM
nails in this study had an average of 1.2 proximal cross
lock screws leading to less stability and more interfragmentary motion than if they had more locking screws.24
The preparation for and insertion of the nails may also
have been factors that stimulated callus in the NAIL
group compared to the PLATE group due to extravasation of medullary contents. This offers another plausible
reason for the differences in callus seen in this study.
Regardless of the reason, the results suggest that in
metaphyseal fractures of the distal femur treated without anatomic reduction and compression fixation which
require external callus to heal, locking plates produce
less callus than IM nails.
One important limitation to the study is that there
were an equal number of nonunions in both groups and
we acknowledge that fracture union is the critical endpoint. However to the extent that union requires callus,
measuring callus could predict subsequent delayed or
nonunions, determine the need for secondary intervention, and assess differences in implants and techniques
with a smaller number of patients than would be necessary for union as an outcome. The differences in callus
between the two groups was also not as clear and distinct
as looking at the series wide average would suggest.
Stabilization of Distal Femur Fractures with Intramedullary Nails and Locking Plates
Several nail cases made a large amount of callus resulting in a wide standard deviation. In addition, in four of
the matched pairs the plated cases actually had more
callus than the nailed cases.This study has several other
limitations. It is a retrospective design and a number of
patients had to be excluded due to inadequate follow up
or poor radiographs resulting in small patient numbers.
The majority of our supracondylar femur fractures have
been treated with locking plates since 2002, which limited the number of nail cases available for study secondary
to a standing hospital policy to destroy radiographs after
seven years of storage. Despite our rigorous matching
criteria it is possible that patient or biological factors
within a matched pair differed enough to effect callus
formation to a greater degree than method of fixation.
Measuring callus on plain radiographs has limitations
including using a two dimensional study to estimate
what is a three-dimensional biological process, however
radiographs have been shown to effectively approximate
callus growth.6,18,27 It is possible that biologic or other mechanical factors not identified in this study contribute to
increased callus formation with IM nails. Therefore the
results of our study should be interpreted with caution
and used as a starting point for further investigation.
In conclusion, in this study locking plates used to
bridge fractures of the distal femur led on average to
less callus formation than IM nails. Further study of
the interaction between construct stiffness and fracture
healing in the distal femur is warranted.
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